Turbochargers operating in conjunction with internal combustion engines increases the power to weight ratio without increasing the weight of the engine. Further a turbocharger ensures complete combustion of the fuel delivered to the engine, thereby reducing the emissions of the engine.
Turbochargers are driven by exhaust gases The idle speed of an exhaust driven turbocharger generally exceeds 30,000 rpm with top speed of about 90,000 to 1,200,000 rpm. During the running (operation) of the automobile engines the lubricant supplied to the turbocharger shaft and bearings by an engine lubrication system. When the oil pump of engine shuts down, the flow of lubricant to the turbocharger centre bearing ceases and the lubricant in the turbocharger oil outlet passage flows towards engine sump located at the bottom of the engine, thereby causes “dry run”. Generally about 20 to 30 seconds may elapse between the engine shut down and the stoppage of the turbocharger during which the center bearing temperature may increase to around 1200.degree. F. Under such conditions the turbocharger bearing assembly carbonizes which can lead to the failure of the bearing(s) and engine.
During the engine start-up, turbocharger oil input line is empty and the time lag between engine starting and pressurized lubricants to reach to the lubricating points is about 4.0 to 4.3 seconds. Further if the operator accelerates the engine.
U.S. Pat. No. 4,513,705 provides an oil storage reservoir & solenoid-actuating valve, wherein the lubricant is stored in the reservoir under pressure. This stored lubricant is part of oil supplied to the turbocharger during high speed/load running of the engine and the same is delivered after shut down and starting phase of the engine by means of actuation of solenoid valve provided at the reservoir opening. This system overcomes the problem of possible turbochargers “dry-run”. The limitation of this system is dependant on the functioning of the solenoid valve and its malfunctioning can lead to the undesired “dry-run” of the turbocharger. Further it leads to problems in interfacing with the system, requires frequent maintenance and servicing resulting in increased cost.
U.S. Pat. No. 6,709,160B1 U.S. Pat. No. 5,993,173, U.S. Pat. No. 5,145,334, U.S. Pat. No. 4,708,602 disclose several options for turbocharger lubrication systems involving using specially designed floating/semi-floating bearings, modifying oil circulation passages in a turbocharger bearing (centre) housing, providing separate and simplified bearing assembly. These patents disclose systems that facilitate effective turbocharger shaft and bearing arrangement lubrication during the running of the engine/vehicle, but do not address the lubrication issues leading to possible “dry-runs” at the start and stop of the engines.
U.S. Pat. No. 4,422,295 discloses a lubricating system for TCs wherein the turbochargers bearings are located at or below the normal level of oil in the lubricating sump for return of oil from the sump to the TC bearings when the engine is not running so as to ensure cooling of the bearing when the engine is not running. However an additional equipment such as a scavenging pump is positioned within the crankcase and is driven by the engine to return the oil from the TC to the crankcase during the running. It is well established that additional equipment in the system increases the possibilities of failure thereby requiring increased maintenance and higher cost of the overall system and operation.
It is a long-standing need in the industry to provide solutions for continuous lubrication of turbocharger shaft and bearings during start and stop operations of TC-Associated systems.